Brexit talks can now start on Monday after Britain bowed to EU pressure for a formal opening to their long-awaited negotiations rather than first holding “technical discussions” between officials.

After a day in which the UK government battled to restore confidence in its crisis-hit Department for Exiting the European Union (DexEU), Theresa May confirmed her team was ready to start next week despite uncertainty over the timing of the Queen’s speech. Whitehall sources said they expect this to mean talks will begin as originally hoped on Monday.

Previously, EU leaders had angered British officials by refusing to allow an initial round of expert discussions first and have insisted on a ministerial presence to show their UK interlocutors can be trusted to speak on behalf of the government.

But efforts to present a united face to Brussels were further called into question by revelations over the departure of one of two DexEU ministers to have left the department. A Whitehall source confirmed that George Bridges had quit against the wishes of secretary of state David Davis, amid reports the well-regarded peer had doubts over government Brexit strategy.

More pressure is likely to build when chancellor Philip Hammond gives a Mansion House speech to the City on Thursday that is expected to emphasise the need for a business-friendly Brexit.

Steve Baker, a prominent remainer who was appointed to replace departing DexEU minister David Jones, insisted this was still compatible with the current approach. Lucy Neville-Rolfe, a Treasury minister appointed to manage liaison with the City on Brexit also announced her resignation.

European frustration over Britain’s muddled approach to Brexit boiled over on Tuesday amid fears that a post-election retreat from hard Brexit by the UK government could deepen the chaotic start to talks.

Guy Verhofstadt, the Brexit coordinator for the European parliament, said at a press conference in Strasbourg that the EU was impatient for the negotiations to start. “We wait for the moment the position of the UK. It is unclear, in any case for me, if the UK government will stick to the line that they announced in the letter of 29 March or whether they will change it taking into account the outcome of the election,” he said.

It is a view matched by an exasperated mood among European diplomats in London. “You [the UK] don’t even know what you want any more, let alone how to get it,” one EU ambassador in London told the Guardian.

Meanwhile, in a sign of growing international tension, a public row erupted when the Danish finance minister warned Britain that the country needed to be realistic about its importance standing alone on the global stage.

“There are two kinds of European nations,” Kristian Jensen, told an audience at the Road to Brexit conference in Copenhagen. “There are small nations and there are countries that have not yet realised they are small nations.” It brought an angry response from the British ambassador to Denmark, Dominic Schroeder, who insisted he saw no sign “of a diminished or diminishing power”.

Whitehall insiders claimed the mood at DexEU remains positive, despite the loss of half its ministers in just 24 hours. “This is what we’ve been working toward and we want to get going too,” said one.

Its permanent secretary, Olly Robbins, met with Michel Barnier, the EU’s chief Brexit negotiator, for preliminary talks on Monday and is said to have made good progress on procedural questions such as the rhythm of talks.

In this first crucial face-to-face encounter, the British diplomats came armed with a plan to start technical talks led by civil servants, to give the prime minister breathing space to fix a deal with the Democratic Unionist party and agree on the programme for the Queen’s speech. Barnier flatly rejected the idea, as he wants to ensure the UK’s chief negotiator has a mandate from the British government before any talks can begin.

It was the first long-awaited meeting between the the British and the EU to discuss ‘talks about talks’, but the EU side initially found the British unable to name a date. Barnier told the British he was open to a number of start dates. “We are flexible, we can do this Thursday, we can do it on Tuesday 20th,” he is reported to have said. As Robbins and Barrow were listening to him running through his diary, in London the government was in disarray over the Queen’s speech. They meet again on Thursday to finalise the formal opening of negotiations.

Senior EU officials are aghast at the chaos in Britain and increasingly concerned that neither the government nor Labour has a clear plan for Brexit. But the confusion is also attracting growing criticism from Brexit supporters in London. “Top Whitehall officials are screaming that DexEU … is a total shambles and disaster is likely: news today just tip of iceberg,” wrote Dominic Cummings, a leading leave campaigner, after the departure of Jones and Bridges.

Signs of a potential shift in the British position grew on Tuesday after a ministerial reshuffle that boosted the proportion of remain supporters. May’s new chief of staff, Gavin Barwell, is a remainer who blames Brexit for costing Tories votes, and the cabinet now also includes ex-Europe minister David Lidington as lord chancellor.

Even Michael Gove, another new arrival and a prominent leave campaigner, said the government should now proceed with the “maximum possible consensus” on Brexit. “We also need to ensure that the concerns of people who voted remain – many of whom now actually want us to press ahead with leaving the European union as quickly and in as orderly fashion as possible – we need to make sure that their concerns are part of our conversation,” he told the BBC.

Former party leader and one-time Eurosceptic William Hague backed some Labour calls for a cross-party commission to take charge of Brexit. Such a move is likely to be welcomed across Europe but the tetchy mood, even among potential allies, suggests there may be limited patience for any major delay.

Jeppe Tranholm-Mikkelsen, the secretary general of the European council and the most senior official under its president, Donald Tusk, appeared to rule out any extension of the two years of negotiations allowed under article 50 of the Lisbon Ttreaty.

He said: “It has to take two years. The formal position is that it would take unanimity [of the EU27] to extend the timeline and I don’t think there will be an interest in doing this because this whole affair is disruptive, uncertainty is disruptive. It takes an awful lot of energy and therefore I don’t think on either side there will be any interest in extending the time period. Therefore we just have to get as far as we can get.”

Speaking at the conference held in the Danish parliament in Copenhagen, he said: “What is Brexit? It’s a good question. Because the slogan Brexit means Brexit, doesn’t mean anything. It’s like breakfast means breakfast.

“I hope that the general election will mean a time out, a pause in their direction they are taking and a chance to rethink the UK and EU27 go on forward.” Jensen added: “I believe Brexit is, sorry to say, a disaster. Not for Europe but for the UK.”

Theresa May confirms start date for Brexit talks after pressure from EU – The Guardian